Project Summary Melanoma is the deadliest skin cancer, with an increasing incidence reported annually. This cancer originates from melanocytes within the basal layer of the epidermis and can quickly progress from nascent tumor formation to distant metastases. This progression is aided by several factors, which can include mutagenesis, microenvironment changes, and loss of cell-cell contact. Under normal conditions within the skin, paracrine signaling between keratinocytes and melanocytes (crosstalk) occurs and is important for regulating melanocyte dendricity and proliferation. Disruption of keratinocyte-mediated signaling results in an altered microenvironment, possibly driving melanoma development. Examination of cancer databases revealed 17% of melanoma patient biopsies showed mutations in desmosomal cadherin, Desmoglein 1 (Dsg1). However, as neither melanocytes nor melanoma cells express Dsg1 or the majority of desmosomal proteins, this suggests a potential role for neighboring keratinocytes to regulate melanoma or melanocytes through a paracrine signaling mechanism. Loss of Dsg1 in keratinocytes revealed significant changes in interleukin 1 family members and pro-inflammatory cytokines, and cytokines, as well as other signaling molecules, have long been implicated in altering the microenvironment and contributing to the development of disease. Melanocytes only exhibited significant increases in cytokine production following co-culture with keratinocytes silenced for Dsg1. Furthermore, Dsg1 is known to regulate epidermal growth factor receptor (EGFR) signaling in keratinocytes in an adhesion-independent manner, a pathway important for the production of pro- inflammatory cytokines. Based on these observations, this proposal tests the hypothesis that Dsg1 regulates interleukin signaling by keratinocytes and that its loss or mutation alters the epidermal microenvironment to promote melanoma development. Aim 1 will determine the effect of mutations of Dsg1 on keratinocyte cytokine production. Aim 2 will determine the effects of altered signaling on melanocyte/melanoma cell behavior. This project will elucidate the mechanisms by which Dsg1 regulates the cellular microenvironment and how this regulation alters the paracrine signaling between keratinocytes and melanocytes to drive melanomagenesis. These studies will be the first to implicate a signaling role for Dsg1 in melanoma.